This invention relates to an indicating composition, indicator strip, process and device for measuring carbon monoxide in the surrounding atmosphere. More specifically, the invention relates to an indicating composition, indicator strip, process and device whereby carbon monoxide can be measured quantitatively.
U.S. Pat. No. 2,487,077, issued to Shepherd on Nov. 8, 1949, discloses a CO indicating composition, process and detection device. The composition consists essentially of a body of purified silica gel freed of substances oxidizable by hot concentrated nitric acid and having combined therein essentially dry residues of impregnation with a solution of palladium sulfate, sulfuric acid and ammonium molybdate, in proportions by weight of about 500 to 1600 parts gel, 5 to 50 parts acid containing about 1 part palladium, and about 10 to 60 parts molybdate. The composition is free of chloride ion.
Canadian Pat. No. 477,288 discloses a granular reagent adapted to undergo a color change in the presence of carbon monoxide consisting of a partly dehydrated granular product prepared by impregnating silica gel with a salt selected from the group consisting of alkali molybdates and tungstates, with a mineral acid, and with palladous halide.
U.S. Pat. No. 3,245,917, issued to Mayo, Jr. on Apr. 12, 1966, discloses a self-regenerating reagent for detecting the presence of carbon monoxide at a relative humidity of at least 20%, consisting essentially of a carrier of silica gel having adsorbed thereon palladium chloride and a regenerating amount of hydrochloric acid.
U.S. Pat. No. 4,043,934, issued to Shuler et al on Aug. 23, 1977, discloses a self-regenerating reagent which, on contact with a reducing gas, oxidizes the gas and is reduced from an oxidized state to a reduced state. The reagent comprises a mixture of a palladium salt, a compound which includes a complex ion of a metal selected from the group consisting of molybdenum, tungsten and vanadium, and a salt of a metal selected from the group consisting of copper, nickel and iron, and a hydrophilic carrier for the mixture. Silica gel is among the possible carriers disclosed and CO detection is one of the uses disclosed for the composition.
U.S. Pat. No. 3,507,623 discloses an article for detecting CO, said article containing an indicating composition such as that disclosed in the Shepherd patent.
U.S. Pat. No. 4,096,227, issued to Gore on June 20, 1978, discloses a process for producing a porous article of a tetrafluoroethylene polymer comprising mixing polymer resin with a lubricant to form a paste, extruding the paste to form an extrudate, removing the lubricant, stretching the extrudate at a high rate (exceeding 10% per second) while maintaining the extrudate at a temperature of about 35.degree. C. to 327.degree. C., then heating the extrudate in a stretched condition to at least 327.degree. C., and cooling the resultant product. The resin can contain a filler, such as asbestos or silica.
Prior art processes and devices for determining the presence of carbon monoxide in the surrounding atmosphere generally rely upon a subjective determination of CO content by comparison of the color of the exposed composition with those of standards. Moreover, for prior art compositions which use silica gel, to insure the removal of interfering impurities, the silica gel must be purified by a time-consuming process involving washing with hot nitric acid and filtration. In addition, prior art devices generally do not measure cumulative exposure to CO and are sensitive to presence of other reducing gases. There is a strong need for a CO indicating composition and/or indicator strip, process and device which readily permit quantitative and cumulative determination of the CO content of the surrounding atmosphere and which are not significantly sensitive to the presence of other reducing gases.